1. Field of the Invention
The present invention relates to a method for the purification of waste air containing biologically decomposable impurities. The waste air is conducted through an absorption tower in which the impurities are absorbed by washing liquid containing an activated sludge. Subsequently, the impurities are biologically decomposed in an activated sludge basin by the microorganisms of the activated sludge. The present invention further relates to an arrangement for carrying out the method.
2. Description of the Prior Art
A method for the purification of waste air containing biologically decomposible impurities is known. In that method, the waste air containing the impurities is conducted through an absorption tower containing packing bodies. An activated sludge washing liquid is conducted through the absorption tower in a countercurrent to the waste air. The activated sludge washing liquid is pumped through the absorption tower in a cycle from an activated sludge basin. When the activated sludge washing liquid comes into contact with the waste air, the impurities contained in the waste air are absorbed by the activated sludge washing liquid. The absorption capacity of the activated sludge washing liquid is dependent upon the solubility of the impurities in the washing liquid and the regeneration of the washing liquid. The absorbed impurities are biologically decomposed in the activated sludge basin by microorganisms of a specific type. The regenerated activated sludge washing liquid is then again capable of absorbing impurities from the waste air.
The known method described above has the disadvantage that the activated sludge basin must be very large if large amounts of impurities are to be decomposed or the residual amount of washing liquid to be removed is relatively large. In addition, this method produces large amounts of biological excess sludge.
It is, therefore, the primary object of the present invention to further develop a method for the purification of waste air containing biologically decomposable impurities, so that the residual amount of washing liquid to be removed is small and only a small amount of biological excess sludge is produced even if large amounts of impurities must be decomposed, while the activated sludge basin remains relatively small. It is another object of the present invention to further develop the method described above, so that it can be used economically for the purification of hot waste air containing resinous condensates from spraying chambers and/or drying chambers of paint spraying plants.